Fatal error: Uncaught Error: Class 'PHPExcel_Writer_OpenDocument_WriterPart' not found in D:\xampp\htdocs\GM\Classes\PHPExcel\Writer\OpenDocument\Thumbnails.php:28 Stack trace: #0 {main} thrown in D:\xampp\htdocs\GM\Classes\PHPExcel\Writer\OpenDocument\Thumbnails.php on line 28